Photocatalysts are known as an effective way to reduce the concentration of gases such as ethylene, and other contaminants in the air, including malodorous gases and microbes. This is desirable because ethylene gas is known to contribute to the aging and senescence of plants. Additionally, having cleaner and better-smelling air is desirable. Various ways of controlling concentrations of ethylene and purifying air have been employed in the past, including filters, oxidizers, and photocatalysts.
Various types of air filter units incorporated with an air filter element have been used for filtering and removing various kinds of powder dust such as pollens, mites, and dust. While such filter units with conventional filter elements can remove powder dust at the intended design efficiency, conventional filter units are incapable of removing materials that exist in a gas phase, including, for example, harmful gases such as volatile organic compounds (VOCs), and malodorant components that produce a bad odor.
Herein, it has been known that such harmful gases and malodorant components can be adsorbed and removed with the use of activated carbon. However, because the adsorption capability of activated carbon is limited, the activated carbon needs to be replaced every time the adsorption reaches saturation. If left unreplaced in the saturated state, the activated carbon would no longer be able to sufficiently adsorb and remove harmful gases and malodorant components, and these materials will respread through the filter unit.
Oxidizers in the prior art suffer from a similar drawback to filters in that they are consumable; they are used up as they work and must be replaced from time to time to maintain their efficacy.
Photocatalysts in the prior art are largely effective in the UV spectrum, although visible spectrum photocatalysts are being synthesized. The increase in indoor lighting that is UV-free leads to a growing need for photocatalysts that are effective in the visible spectrum.
The discussed shortcomings of the technologies currently in use show there is a need for a more effective visible-spectrum photocatalyst.